The invention relates to an electro-surgical instrument for high-frequency cutting and high-frequency coagulation having two electrodes, spaced apart from each other by insulating material, particularly an insulating layer, which at the proximal end of the instrument are each connected during operation to an outlet of a high-frequency supply device, with a first electrode surface of a first electrode being designed such that together with the second electrode it can be used as the cutting electrode.
The cutting electrode is sometimes also called the active electrode. This is the electrode where preferably the electric current necessary for cutting ignites through the tissue.
Electro-surgical instruments with bipolar electrodes are known in many various embodiments.
They have been used for the coagulation of tissue for quite some time. This purpose is served, for example by bipolar tweezers or bipolar electrodes with poles fixed at a distance from each other and having approximately the same size, i.e. contact area to the tissue.
Bipolar electrodes are also known for electro-surgical cutting. In order to create a cut both electrodes coming into contact with the tissue must be of unequal sizes, i.e. embodied asymmetrically. In an asymmetrical embodiment the cut develops at the smaller electrode, which creates a spark by the higher current density and thus initiates the cut. Such an electrode arrangement is bad for coagulation, because by the development of sparks excessive temperatures are reached too fast. Coagulation electrodes in turn are unsuitable for cutting because by the equal size of the electrodes no particular high current density develops at either of the electrodes and thus no spark can develop.
An electrode particularly for bipolar cutting is described e.g., by Thorne et al. in US 2005/0283149 A1. Here, the cutting electrode is embodied in the form of a needle which is mounted in a hemispherical second electrode element and insulated therefrom. This arrangement can easily initiate a cut; however the coagulation of e.g., a vessel bleeding into the edge of the cut will hardly be possible.
A bipolar electrode in the form of knives is also described by Goble in U.S. Pat. No. 6,832,998 B2 for bipolar cutting. Here, a bigger and a smaller electrode are arranged beside each other and separated by an insulator. Furthermore, it is explained that the two electrodes are not only be different with regard to their size, but also with regard to their constitution, particularly their thermal conductivity. This further favors the simplicity and regularity of the cut at the smaller electrode. This electrode arrangement is also rather unsuitable for coagulating tissue. In order to overcome this, U.S. Pat. No. 6,832,998 B2 points out that it may be advantageous to provide a third electrode on the knife, which is electrically insulated from the other two electrodes. However, here it is necessary for the electro-surgery—generator to be able to switch between the electrodes and thus to stop supplying the formerly “active” electrode with electric current, but instead to supply the third electrode with the counter pole of the first electrode in order to use two electrodes that are approximately equal in size for coagulation.
In U.S. Pat. No. 6,942,662 B2 Goble et al. once more discuss the necessity of a third electrode in order to allow also to coagulate via the bipolar cutting knife. Here again, a switching mechanism between the different pairs of electrodes, installed in the generator, is a requirement for the operation of said instrument.
In a modification thereof, Goble discusses in U.S. Pat. No. 7,147,637 B2 a bipolar gripping or clamping instrument, with all electrodes being located on one of the two jaw parts and the second jaw part being completely electrically insulated at the gripping surface. Here again, the arrangement requires three electrodes, and again a respective device must be provided in the generator to switch back and forth between the electrodes.
In US 2005/0283151 A1 Ebbutt et al. discuss a bipolar cutting knife, which largely resembles in its shape a classic knife. Here, a circumferentially extending thin electrode, representing the active electrode, cuts against the electrodes arranged on the two sides of the knife representing the passive electrodes. Here it is again provided to achieve a planar coagulation by placing one of the two sides of the knife onto the tissue so that a total of three electrodes are provided, with once more the two electrodes arranged on the area not connected to the third cutting electrode being activated, which in turn requires a switching mechanism in the generator.
In U.S. Pat. No. 7,255,696 B2 Goble et al. describe a bipolar cutting and coagulation instrument in form of a hook. Again, three electrodes are provided on the instrument, in which the same restrictions apply as in similar arrangements already in circulation. Additionally, in U.S. Pat. No. 7,255,696 a liquid circuit is provided inside the head of the electrode, which cools the two large-area electrodes.
In U.S. Pat. No. 6,110,196 Mueller et al. describe a bipolar cutting instrument, with the two electrodes being arranged one behind the other along an axis according to the direction of cutting. This can occur, e.g., by a loop-shaped wire electrode, which is interrupted at one point located in the direction of cutting and is electrically divided into two parts. It may also occur by a wire positioned circumferentially around a ceramic knife, which in turn is interrupted at one point and with the two wire elements representing the two electrodes. Coagulation can hardly be achieved with such an arrangement because the surface of the electrodes is very small and thus the current density at the electrodes is so high that a cutting rather than a coagulating effect is yielded. Additionally, the coagulation zone would be so small that sufficient closure of vessels would be impossible even in cases of relatively small vessel diameters. Furthermore, during the cutting process the thin electrodes heat up, which is not hindering the cutting process per se, however during coagulation it rapidly leads to a layer of denaturized protein, acting as an insulator, precipitating on the electrodes and thus the effectiveness of the coagulation is further reduced. In order to overcome this, Mueller et al. suggest, for example, to arrange two electrodes (e.g., by metal-coating a ceramic surface) on the back of a so-called carrier element in order to allow coagulation to be carried out by rotation of the instrument and the placement of this surface in the area to be affected. It must be expected once more that the coagulation electrodes heat very quickly due to the low material mass thereof in this design the coagulation remains insufficient. Furthermore it is necessary to provide additional electrodes, not connected in one piece to the cutting electrodes, on an insulating carrier element.
In US 2003/0040744 A1 Latterell et al. suggest a bipolar tubular instrument for cutting and coagulation. Once more an arrangement of three electrodes is used. Two of them form a hemisphere with a slot therebetween and are used for coagulation. In the slot itself, a third electrode is located in a displaceable fashion in the form of a hook, which can cut when active, while now the two other ones switched together acting as neutral. A mechanism is located inside the handles to displace the hook continuing in the tubular shaft. In this solution, once more a switching mechanism must be provided in the generator in order to allow the use of the instrument both for coagulation as well as for cutting. Furthermore, it is necessary to displace the described hook, which operates as the cutting electrode. Such a device renders the production of the instrument more expensive and still requires the user to manipulate the instrument in order to switch from cutting to coagulation and vice versa.
Rydell describes a bipolar tubular cutting instrument in U.S. Pat. No. 5,282,799. In another embodiment described a coagulation device is provided. Here, different than in Mueller et al. in U.S. Pat. No. 6,110,196, two parallel loops are used as electrodes. It is problematic here, that it is not clearly defined at which of the two loops the cut will begin, because due to the loops and thus the same current density the two electrodes are only activated when a different field distribution is enforced, and then the cutting starts. This can occur e.g., by placing first one of the two loops onto the tissue and then the second loop is brought closer. The cutting will then form at the second loop, because at the moment the second loop contacts the tissue here the electric field strength is greater than in the loop already located on the tissue. This aggravates the handling of the instrument and results in less precision during operation.
The U.S. Pat. No. 5,282,799 also describes an embodiment with additional large-area coagulation electrodes being applied proximally in reference to the two cutting loops on the insulator from which the loops exit, e.g., by way of metal-coating a ceramic surface. Here it is problematic that during placement of the two projecting loops onto the place to be coagulated they are obstructive as long as the loops project from the insulating body at the distal area. The distal end of a surgical instrument is called the patient-side end in this document, while the proximal end is the opposite end. In this document the surgical instrument is therefore considered the extended arm of the user, and the terms proximal and distal are understood and used in reference to the body of the user.
Furthermore, in the U.S. Pat. No. 5,282,799 the loops are electrically active and thus they develop either a coagulating effect or, due to their relatively small surface, perhaps even a cutting effect at another location of the tissue. In order to overcome this, U.S. Pat. No. 5,282,799 suggests retracting the loops into the insulating body. Although this facilitates the application of the coagulation electrodes, however it renders the production more expensive and burdens the user with a more complicated handling. Furthermore, the disadvantage remains that, as in the patent of Mueller et al. U.S. Pat. No. 6,110,196, the mass of the metal-coated coagulation electrodes is very small and that thus they would likely heat up very quickly and lead to insufficient coagulation.
Ciarrocca describes a bipolar coagulation and cutting electrode in U.S. Pat. No. 7,195,630 B2. Here, the surface of the two bipolar electrodes is increased and/or reduced, respectively, by a displaceable “converter element”. For coagulation the “converter element” is made to contact the smaller of the two electrodes to enlarge its surface. The “converter element” is made to electrically contact the larger of the two electrodes for cutting, in order to enlarge it even further and thus to achieve a distinct asymmetry between one electrode and the other. This way the cut is created at the smaller electrode. U.S. Pat. No. 7,195,630 B2 only requires two electrodes, which are “converted” via a mechanical device into coagulation and/or cutting electrodes. However, for this purpose a mechanical device is necessary, rendering the production of the instrument more expensive and setting certain limits regarding the miniaturization of the instrument. Furthermore, only an essentially tubular instrument is described.
In U.S. Pat. No. 4,202,337, Hren et al. describe a bipolar electro-surgical knife. Here, a pole arranged circumferentially around a ceramic knife, the cutting electrode with a relatively small surface is used against the electrode elements applied on the flanks of the knife, which form the passive electrode. The passive electrodes on the flanks of the knife are applied in lines. Due to the fact that only two poles are provided either all electrode lines on the flanks of the knife combined form one electric pole or one or more of these lines are connected to the other pole, i.e. the cutting electrode. In the latter case, in turn, no electro-surgical cut will develop because by the switching of one of the electric lines of one or both of the flanks to the “active electrode,” its surface, being in contact with the tissue, becomes so large that no spark will develop because the current density becomes too low. To this extent, the electrode arrangement is advantageous for cutting, however unsuitable for coagulation or vice versa.
Fleenor et al. describe a tubular bipolar cutting instrument in U.S. Pat. No. 5,484,435. It comprises two electrodes, one of which having a smaller surface than the second one so that the first one forms the active electrode and the second one the passive electrode. In this solution it is impossible to vary the size of one or both of the electrodes rendering the instrument limited to the electro-surgical cutting and thus subjecting it to the same limitations as e.g., the instrument described in US 2005/0283149 (Thorne et al.). In the aspect of a displaceable active electrode described, which may also be embodied as a hook, it resembles the instrument of US 2003/0040744 (Latterell et al), however, it differs therefrom in that only two electrodes are provided which is advantageous in that the instrument can be operated with any arbitrary generator, but is not very well suitable for the coagulation of tissue.